It is well known to utilize mirrors and lenses to reflect and focus light rays and in particular it has become important to utilize concepts in the efficient capitalization upon solar energy in the face of our depleting natural resources.
One of the concepts which is currently undergoing experimentation is the utilization of a large number of mirrors to reflect sunlight or solar energy to a central generator or boiler which will utilize substantially all of the reflected light and convert it to more common energy forms. It becomes apparent that there are locations where there is not enough unobstructed surrounding area to accommodate a sufficient number of planar mirrors to concentrate the solar energy and therefore, it is necessary to utilize a concave reflecting and/or focusing system to develop the necessary heat. The expense of inflexible concave mirrors of a large scale is prohibitive, and therefore, a focusing membrane appears to be a practical approach. As will be noted hereinafter, there are previous examples in the patented art of mirrors which are constructed of metalized fabric that are formed into a configuration which serves to concentrate the reflected light.
One of the problems inherent with using a contour-controlled metalized membrane, although substantially less expensive than an equivalent glass mirror, is that it is subject to distortion and change with a change in the angle to the local gravitational field or by changes in relative atmospheric pressure. Various attempts have been made, as illustrated hereinafter, to assure that the configuration of the concentrating and reflecting surface comprising a metalized membrane be held uniform, each of these attempts as will be obvious, have inherent deficiencies. It is believed the present invention overcomes the deficiencies of the prior art.
In general, the present invention deals with a flexible metalized reflective membrane capable of being focused upon a target and which is able to maintain, even though orientation is varied, a controlled curvature. The mirror, in its entirety, comprises a pair of air impermeable membranes closing the front and back surface formed by a hoop type framework thus forming an enclosed area. A sensing member in the form of a capacitive plate is suspended between the membranes and by control apparatus, the relative pressure between the membranes with respect to the surrounding or ambient pressure is adjusted to maintain the membrane in a constant curvature. The curvature or location of the membrane is measured by electronically determining the distance between the capacitive plate and the metalized membrane. A guard electrode is utilized to reduce capacitance variation.
Prior art known to the inventor includes U.S. Pat. No. 3,001,196 granted Sept. 19, 1961 to McIlroy et al wherein the pressure within a chamber behind a direct beam antenna is varied to change the shape of the antenna and thus the shape of the beam.
U.S. Pat. No. 3,031,928 granted May 1, 1962 to Kopito teaches the concept of utilizing a capacitive probe to determine the location of the reflective surface and a control system to alter the relative pressure and thus change the location of the reflective surface.
U.S. Pat. No. 3,254,342 granted to Miller on May 31, 1966 teaches the concept of an antenna system wherein an intermediate reflector has its shape changed to vary the band width. The secondary reflector has its shape changed by utilization of a flexible reflector surface and the introducation of air or some other formative agent behind said reflector.
U.S. Pat. No. 3,273,157 granted to Kirstein on Sept. 13, 1966 utilizes a pneumatic control system for varying the shape of a radar antenna.
U.S. Pat. No. 3,289,205 granted Nov. 29, 1966 to Kampinsky teaches a method of fabricating a large surface reflector as well as means for determining the electromagnetic characteristics of the surface.
U.S. Pat. No. 3,325,887 granted to Bird et al on June 29, 1967 teaches a method of fabricating a parabolic air inflated fabric structure as well as the structure itself.
U.S. Pat. No. 3,493,290 granted to Traub on Feb. 3, 1970 teaches the concept of a reflective membrane serving as one plate of a capacitor used in determining the location of the reflective membrane.
U.S. Pat. No. 3,510,205 granted to Schiffman et al on May 5, 1970 teaches the concept of a mirror which is mechanically moved in response to a photocell circuit to dim the reflection.
U.S. Pat. No. 3,514,776 granted to Mulready on May 26, 1970 teaches the utilization of an adjustable, reflecting concave face for aiming a laser beam. The mirror is formed by a plate mounted in a housing and has its configuration adjusted by forces acting between the surface and the housing.
U.S. Pat. No. 3,623,793 granted to Merten et al on Nov. 30, 1971 teaches the concept of an adjustable magnifying mirror wherein a flexible reflector is mounted within an air tight seal and the mirror is changed in configuration by means of a differential pressure created between the rear portion of the mirror and the atmosphere.
U.S. Pat. No. 3,893,755 granted to Cobarg et al on July 8, 1975 teaches the concept of an adjustable focal length mirror wherein the focal length of the mirror is changed by moving a supporting frame sealingly mounted within a tubular member to change the relative pressure.
U.S. Pat. No. 3,936,159 granted to Pavenick on Feb. 3, 1976 teaches the concept of forming a heat shrunk plastic film mirror wherein the shrinking of the film urges the resilient upper section of the frame inwardly causing the film to be maintained in the stage of constant tension.
U.S. Pat. No. 3,972,600 granted to Cobarg teaches the concept of a mirror having an adjustable focal length wherein the relative pressures on either side of the mirror within a sealed compartment may be altered thereby changing the configuration of the mirror.
U.S. Pat. No. 3,623,796 granted to Schweiger on Nov. 30, 1971 teaches the concept of a mirror fabricated with a light reflective resilient membrane sealingly secured to a housing and a pump capable of creating a partial vacuum to change the shape and thus adjust the focal length of the mirror.
With the above noted prior art and inadequacies in mind, it is an object of the present invention to provide a simple, inexpensive means for providing a focused reflective surface and a reliable means for maintaining the proper focus upon that reflective surface even though varying forces are generated by a difference in attitude of the reflector or by a change in ambient conditions.
It is another object of the present invention to provide a unique control system for maintaining the proper focus of a flexible reflector comprising a capacitive member mounted within an enclosed area adjacent the reflective surface and measuring the distance between the capacitive member and the reflective membrane. Any change in relative position alters the capacitance and the control system thus determines the variation in pressure necessary within the enclosed area to maintain the proper focus of the reflective surface.
It is another object of the present invention to provide a large scale flexible reflective surface wherein the control for the focal configuration is substantially independent of the relative orientation of the reflective surface or of the differentials caused by changes in atmospheric conditions.
Still a further object of the present invention is to provide a capacitive control system for the focal length of a flexible reflective system wherein the capacitive member is electrically isolated from the reflective member and its supporting structure although suspended within the assembly.
A further object of the present invention is to provide a lightweight membrane covering the rear of the focusing mirror cavity, metalized to be electrically conductive, the membrane being electronically driven to the same potential as the capacitive member and shielding the latter from all variations in external electric field gradients, thus removing any environmental disturbance to the measurement of capacitance of the reflecting membrane.